The present invention relates to a roll for a corrugated board manufacturing machine.
A corrugated board manufacturing machine comprises at least two fluted rolls engaged one in the other and between which a sheet of paper is passed so as to form corrugations therein.
An important technical progress in the design of corrugated board manufacturing machines, commonly termed "corrugators", consisted in maintaining the sheet of paper subjected to the corrugation, no longer by segments outside the fluted corrugation rolls, but by means of a source of low pressure, which creates a phenomenon of causing the sheet of paper to be held closely against the cylinder by suction.
There has thus been proposed in the document FR-8-2348817 a corrugated board manufacturing machine whose fluted roll comprises a shell defining an inner suction chamber permanently connected to a source of low pressure and provided with a series of suction apertures opening onto the peripheral surface of the shell.
Although the solution proposed in the document is satisfactory as concerns the maintenance of the sheet of paper on the outer peripheral surface of the shell by suction, it nonetheless has several drawbacks. The lower corrugating roll, having a suction arrangement, is not equipped with heating ability enabling a correct thermo-forming of the corrugations of the sheet of paper to be effected. This absence of heating requires arranging the passage of superheated steam through a hollow inner portion of the upper corrugating roll, similar to the suction chamber of the lower corrugating roll. The phase of the heating of the sheet of paper therefore does not coincide with the phase for mechanically forming the corrugations. Moreover, this document proposes no simple and effective technical way of connecting the inner chamber of the lower corrugating roll to a source of low pressure, the sectional view of the lower corrugating roll shown in the document merely being a diagram for illustrating the principle of operation thereof.
Document FR-B-2 404 709 describes and illustrates a corrugating machine whose second corrugating roll, on the semi-circumference of which the sheet of paper is wound, comprises an inner heating chamber in which steam circulates. The system for maintaining the sheet of paper on the fluted roll by the effect of suction is constituted by an arrangement outside the roll comprising, in particular, an assembly of lateral, front and rear walls defining an outer suction chamber surrounding the other semi-circumference of the fluted roll, the suction means further comprising heating means for avoiding differences of expansion between the various component elements of the assembly. The solution proposed in this document is complex and costly, in particular in that it requires the use of many components independent of the roll which must be arranged with precision on the periphery of the latter.
The document FR-B-2 645 027 describes and illustrates a corrugating machine whose lower fluted roll comprises an inner heating chamber in which saturated steam circulates, this chamber being defined by a cylindrical shell whose outer peripheral surface is fluted, a large number of longitudinal ducts being drilled in the body of the shell so as to be evenly spaced apart throughout the width of the cylinder, i.e. throughout the effective fluted length of the latter, and which are connected to a source of low pressure. Each longitudinal duct is connected to the outer fluted peripheral surface of the shell through axial apertures which have a smaller diameter and are drilled evenly along each duct.
This arrangement, although it has the advantage of grouping within the fluted roll the paper sheet heating and suction functions, nonetheless has many drawbacks. The connection of each longitudinal duct with a source of low pressure, such as for example a vacuum pump, is achieved by means of a semi-circular shaped sector which bears on an end edge surface of the shell and in front of which pass in succession the longitudinal ducts spaced apart on a semi-circumference of the roll and which performs the function of a rotary depression distributor. This design requires the use of a very powerful source of low pressure having a high rate of flow, since the longitudinal ducts are alternately put back into communication with the ambient air, which fills them, and then put back in communication with the source of depression.
More basically, this design in which the suction ducts are disposed on the periphery of the roll and in which the heating source is a cylindrical chamber within the shell, does not permit ensuring an effective heating of the sheet of paper in contact with the roll. Indeed, the circulation of air in the longitudinal outer peripheral ducts tends to cool the fluted roll in opposition to the heating action of the circulation of steam in the inner chamber, this cooling also having a result of producing a phenomenon of a very great amount of condensation of water inside the inner heating chamber. The condensed water driven in rotation forms an "annular shell of water" which provides an insulation and causes a large temperature gradient between the steam and the outer shell, which is made from metal, having an adverse effect on the thermal conductivity efficiency of the assembly.